1. Technical Field
The invention relates to loudspeakers and more particularly to loudspeakers comprising panel-form acoustic radiating elements.
2. Background Art
It is known from GB-A-2262861 to suggest a panel-form loudspeaker comprising:
resonant multi-mode radiator element being a unitary sandwich panel formed of two skins of material with a spacing core of transverse cellular construction, wherein the panel is such as to have ratio of bending stiffness (B), in all orientations, to the cube power of panel mass per unit surface area (xcexc) of at least 10;
a mounting means which supports the panel or attaches to it a supporting body, in a free undamped manner;
and an electromechanical drive means coupled to the panel which serves to excite a multi-modal resonance in the radiator panel in response to an electrical input within a working frequency band for the loudspeaker.
U.S. Pat. No. 3,164,221 of RICH discloses a low frequency loudspeaker comprising an enclosure, an acoustic radiator in the enclosure, a compliant suspension mounting the radiator in the enclosure for pistonic movement, and pistonic drive means for varying the air pressure in the enclosure to cause the radiator to move pistonically.
U.S. Pat. No. 3,247,925 of WARNAKA discloses what purports to be a low frequency resonant panel loudspeaker mounted in a chassis and excited by an electromechanical transducer mounted on the chassis.
Embodiments of the present invention use members of nature, structure and configuration achievable generally and/or specifically by implementing teachings of our parent application Ser. No. 08/707,012. Such members thus have capability to sustain and propagate input vibrational energy by bending waves in operative area(s) extending transversely of thickness often but not necessarily to edges of the member(s); are configured with or without anisotropy of bending stiffness to have resonant mode vibration components distributed over said area(s) beneficially for acoustic coupling with ambient air; and have predetermined preferential locations or sites within said area for transducer means, particularly operationally active or moving part(s) thereof effective in relation to acoustic vibrational activity in said area(s) and signals, usually electrical, corresponding to acoustic content of such vibrational activity. Uses are envisaged in parent application Ser. No. 08/707,012 for such members as or in xe2x80x9cpassivexe2x80x9d acoustic devices without transducer means, such as for reverberation or for acoustic filtering or for acoustically xe2x80x9cvoicingxe2x80x9d a space or room; and as or in xe2x80x9cactivexe2x80x9d acoustic devices with transducer means, such as in a remarkably wide range of sources of sound or loudspeakers when supplied with input signals to be converted to said sound, or in such as microphones when exposed to sound to be converted into other signals.
This invention is particularly concerned with active acoustic devices in the form of loudspeakers.
Members as above are herein called distributed mode acoustic radiators and are intended to be characterised as in the above parent application and/or otherwise as specifically provided herein.
The invention is a loudspeaker comprising an enclosure, an acoustic radiator in the enclosure, a compliant suspension mounting the radiator in the enclosure for pistonic movement relative thereto, and means for varying the air pressure in the enclosure to cause the radiator to move pistonically, characterised in that the radiator is a member having capability to sustain and propagate input vibrational energy by bending waves in at least one operative area extending transversely of thickness to have resonant mode vibration components distributed over said at least one area and have predetermined preferential locations or sites within said area for transducer means and having a transducer mounted wholly and exclusively on said member at one of said locations or sites to vibrate the member to cause it to resonate forming an acoustic radiator which provides an acoustic output when resonating. The air pressure varying means may comprise an air pump. The air pump may comprise a subsidiary enclosure, a pistonic driver mounted in the subsidiary enclosure and means coupling the interiors of the respective enclosures such that air pressure waves produced by motion of the pistonic driver are transmitted to the said enclosure. Acoustically absorbent means may be provided in the said enclosure and/or in the subsidiary enclosure. The radiator may comprise a lightweight cellular core sandwiching a pair of high modulus lightweight skins.